Seizures in Horses

Q. I'm interested in purchasing a horse which has a history of seizures. What could they be caused by, are there different forms, and is there anything I can do to prevent them from happening again?

A. First of all, you would need a veterinarian's assessment of the horse and the predisposition to seizures. The history of the individual horse is extremely important. A horse, like any other animal, can have a true or a false seizure. For example, a dog with an ear infection can be put on a table, and the animal might fall over, presenting what looks like a seizure. Horses with an inner ear infection can look the same, with possibly a loss of balance, while retaining their normal strength. Narcolepsy, characterized by uncontrolled episodes of sleep and loss of muscle tone (cataplexy), can look like a seizure as well. The horse appears as if it is passing out and falling down. A true seizure deals with electrical activity within the cerebral cortex of the brain.

The problem with diagnosing seizures is that a veterinarian usually isn't examining the horse while it is having a seizure. It is rare that the veterinarian actually sees the seizures, and this usually happens only if the onsets are frequent or perpetual.

The causes of seizures are quite varied. Horses do get epilepsy. Some seizures are a metabolic reaction, characterized by convulsions, which are of a short duration. The horse needs oxygen and glucose to conduct electrical activity in the brain correctly. Neither is stored in the brain. The horse might be hypoglycemic (low blood glucose), resulting in a seizure.

It is not entirely uncommon for foals to have seizures from metabolic imbalances. The foal can become hypoxemic, suffering lack of oxygen to the brain, and respond with a seizure.

Kidneys are the filters of the body. There might be a kidney disorder in the horse that prevents the animal from retaining the electrolytes for the brain. Other causes of seizures might be an invasion of infections in the brain (meningitis, for example), bacteria, viruses, or protozoal myelitis. Head trauma might cause excessive hemorrhage to penetrate the brain, thus spurring a seizure.

Masses in the brain, such as tumors, disrupt the normal electrical activity of the brain and can trigger seizures. Abscesses have been known to form in the brain as a result of strangles (Streptococcus equi) and have the same potential effect.

Toxicities and reactions to drugs can cause seizures. For example, a reaction to procaine penicillin, lead poisoning, or other heavy-metal poisonings can trigger seizures. Occasionally you will hear about a horse which, upon receiving an injection, responded with a seizure. This usually is caused by the injectable's mistakenly entering the carotid artery. Moldy corn and locoweed toxicity also can cause seizures.

The seizure itself can be perpetual, sustained, or intermittent. Seizures are predominantly intermittent, and rarely sustained. A spinal fluid sample or bloodwork will alert the veterinarian as to whether there is inflammation, infection, or electrolyte imbalances.

Radiographs give practitioners the ability to see old skull fractures. The majority of epilepsy cases stems from previous trauma to the brain. MRI scans and CT scans for the head are largely unavailable because of the sheer size of the animal's head and the costs involved in these procedures; however, foals are small enough to undergo these diagnostic tests.

An electrical encephalogram (EEG) can be used to view the brainwaves or electrical impulses of the brain. While not used to diagnose the cause of a seizure, EEGs readily can confirm activity that causes seizures. The Ohio State University is one of the few places a horse can undergo an EEG exam.

The prognosis of the horse with seizures will vary, depending on the cause of the seizure. A young foal's prognosis normally is good, as the foal usually will outgrow the symptoms and go on to perform normally. There are many things to consider in the prognosis of an adult horse affected by seizures. You must consider the danger to the people working with the horse; caution should be taken, as a 1,000-pound animal in a seizure can inflict serious harm to his handlers and himself.

Prognosis for horses which have seizures as a result of viral infections, such as herpes, is dependent upon the severity of the infection. Treatment only allows the owner to maintain the horse, not "cure" him.

A horse affected by a bacterial cause of seizures can be treated with antibiotics. The bacteria are detectable in the blood/spinal samples, and the respective medication can clear up the infection, whether it be bacterial meningitis or something of a protozoal nature. Fungi within the brain are rare. Prognosis is normally poor, as it is very difficult for anti-fungal drugs to reach adequate levels in the deep crevices where the fungi reside in the brain. Anticonvulsant medications might manage seizures in some horses.

Surgery, whether to drain the abscess or remove a mass in the brain, is very uncommon. Although skull trauma might fracture and dislodge a piece of bone in an area where a surgeon can remove the chip, fractured parts usually are not accessible for the surgeon to reach.

Once again, diagnosis and prognosis of the horse with seizures are highly dependent on the background of the horse. Delve deep into the horse's history--daily habits, previous injuries, and living situations and make sure an experienced veterinarian knows these facts. It remains unnerving to witness a seizure in a horse, but there is hope in understanding, managing, and solving the problem.

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